Flexible support structure for vibration testing

ABSTRACT

A vibration testing device for supporting items to enable them to be vibrated in three orthogonal directions and pivoted about a vertical axis while maintaining them level, or horizontal, comprising an item-supporting platform surrounded by an intermediate member which, in turn, is surrounded by an outer member. A first group of resilient thin walled cylinders support the platform on the intermediate member, all of these cylinders oriented with their axes horizontal and extending circumferentially about the platform. A second group of resilient thin-walled cylinders support the intermediate member on the outer member, these cylinders all oriented with their axes vertical. Shaking forces are transmitted to the platform through a structure which includes an inner shaft attached to the platform, a cylindrical surrounding member which can be driven, and a group of resilient thin-walled cylinders whose axes extend parallel to the shaft and which are attached at diametrically opposite sides to the shaft and surrounding member, respectively.

ts-see 5R United St:

Deckard A.

[54] FLEXIBLE SUPPORT STRUCTURE FOR VIBRATION TESTING [72] Inventor:Charles E. Deckard, Huntsville, Ala.

[73] Assignee: Wyle Laboratories,

Calif.

[22] Filed: Aug. 3, 1970 [21] Appl. No.: 60,674

El Segundo,

[56] References Cited UNITED STATES PATENTS 3,318,139 5/1967 Crook..73/7l.6

Primary ExaminerRichard C. Queisser Assistant Examiner-John P. BeauchampAztorneyLindenberg, Freilich and Wasserman [451 Sept. 19, 1972 [57]ABSTRACT A vibration testing device for supporting items to enable themto be vibrated in three orthogonal directions and pivoted about avertical axis while maintaining them level, or horizontal, comprising anitem-supporting platform surrounded by an intermediate member which, inturn, is surrounded by an outer member. A first group of resilient thinwalled cylinders support the platform on the intermediate member, all ofthese cylinders oriented with their axes horizontal and extendingcircumferentially about the platform. A second group of resilientthin-walled cylinders support the intermediate member on the outermember, these cylinders all oriented with their axes vertical. Shakingforces are transmitted to the platform through a structure whichincludes an inner shaft attached to the platform, a cylindricalsurrounding member which can be driven, and a group of resilientthin-walled cylinders whose axes extend parallel to the shaft and whichare attached at diametrically opposite sides to the shaft andsurrounding member, respectively.

5 Claims, 7 Drawing Figures PATENTED SEP 19 1972 SHEET 1 BF 2 MMLWW I,Q-rTOQJEYS PATENTEDSEP 19 I972 SHEU 2 [IF 2 QT OEAIEYS FLEXIBLE SUPPORTSTRUCTURE FOR VIBRATION TESTING BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to supporting structures and, moreparticularly, to structures which allow freedom of movement within alimited range in selected directions.

2. Description of the Prior Art There are many types of machines whichrequire the support of a member in a manner that enables resilientdisplacement in certain directions but great resistance to displacementin certain other directions. One example of an application is invibration testing where it is necessary to determine the endurance ofequipment when vibrated in certain directions,- and where it isdesirable to prevent vibrations in certain other directions. Forexample, some types of equipment are vibration tested for vibration inthree orthogonal directions and about a vertical axis, but the equipmentmust be maintained in a level orientation throughout the test. Whileordinary springs or elastomeric pads can be used for resilient supportand a series of guide rails can be used to limit vibration to onlycertain directions, this type of equipment is relatively complex andexpensive. In conducting tests on vibration testing apparatus, it isalso necessary to provide means for imparting vibrations to theequipment-holding platform from conventional piston-type oscillators, orthe like, in a manner that enables forces to be applied in one linealdirection without hampering vibrations in other directions.

SUMMARY OF THE INVENTION In accordance with the present invention,apparatus is provided for enabling resilient deflection of a member froma neutral position in selected directions while strongly resistingdeflections in other directions. The apparatus includes an inner membersurrounded by an outer member, and four resilient thin-walled cylindersdisposed between the members. The cylinders enable twisting and radialtranslation of the inner member with respect to the outer member whileproviding a spring-like action tending to return the inner membertowards its original neutral position. However, the cylinders stronglyresist any movement in the inner member in a direction parallel to theaxes of the cylinders.

In accordance with one embodiment of the invention, a vibration table isprovided which includes a platform, an intermediate member surroundingthe platform, and an outer member surrounding the intermediate member. Afirst group of resilient thin-walled cylinders is disposed between theplatform and intermediate member, and a second group of resilientthinwalled cylinders is disposed between the intermediate and outermembers. The platform is horizontal and each of the first group of.cylinders extends circumferentially about the platform with its axishorizontal and with diametrically opposite sides of the cylinderrespectively joined to the platform and intermediate member. Each of thesecond group of cylinders extends with its axis vertical and withopposite sides respectively joined to the intermediate and outermembers. The platform can vibrate in any horizontal direction as well asup and down, and can vibrate about a vertical axis. However, theplatform strongly resists any tilting and therefore remains level, orhorizontal.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aflexure bearing assembly constructed in accordance with one embodimentof the present invention;

FIG. 2 is a plan view of the bearing assembly of FIG.

FIG. 3 is a view similar to FIG. 2, but with the shaft of the bearingassembly pivoted from its neutral position;

FIG. 4 is a view similar to FIG. 2, but with the shaft displaced to oneside from its neutral position;

FIG. 5 is a perspective view of a vibration table constructed inaccordance with another embodiment of the invention;

FIG. 6 is a perspective view of a vibration table constructed inaccordance with still another embodiment of the invention; and

FIG. 7 is a side elevation view of the vibration table of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a bearingassembly which includes an inner member or shaft 10, an outer member 12surrounding the shaft, and four cylinders l4, l6, l8 and 20 disposedbetween the shaft and outer member. The shaft 10 and outer member 12both are centered on a vertical or Y axis and the axes of the fourcylinders also extend parallel to the Y axis. Each cylinder isthinwalled and is constructed of a resilient material. Diametricallyopposite sides of the cylinders are fixed to the shaft 10 and outermember 12, respectively.

FIG. 2 is a top view of the bearing assembly, showing its configurationwhen the shaft 10 is in an undeflected or neutral position. FIG. 3illustrates the bearing assembly when the shaft 10 has been pivotedabout the vertical or Y axis. It can be seen that each of the cylindersdeforms into a non-cylindrical shape. While the cylinders resist suchdeformation, they resist it with only a moderate spring force, so that apivotal deflection of several degrees can be readily obtained and yetthe shaft is resiliently urged towards its neutral position with asubstantial force. The force urging the shaft back towards its neutralrotational position increases very greatly after several degrees ofpivoting past the neutral position, as the cylinders become greatlydeformed from a cylindrical shape. Thus, while small deflections can bereadily made, the spring constant tending to return the shaft to itsneutral position increases as deflection increases, and rotationaldeflections can be kept within a limit of several degrees.

FIG. 4 illustrates a situation where the shaft 10 is deflected to oneside, or along the Z direction, which tends to bring the shaft closer toone portion of the outer member 12. Such deflection causes the fourcylinders 14-20 to be deformed into somewhat of an oval shape. Thissideward deflection is resiliently resisted by the cylinders, with onlya moderate spring constant for slight deflections and with the springconstant increasing as the deflection increases. Thus, the bearingapparatus enables slight sideward or radial deflections to be made,which are resiliently resisted, while strongly resisting very largesideward deflections. if it is attempted to cause sideward deflection atonly one end of the bearing member, such as its top or bottom end (wherethe Y axis is the vertical), this will be strongly resisted. Therefore,the shaft it) cannot pivot about the horizontal axes X and Z.

While the bearing assembly allows resilient pivoting about one axis (theY axis), and allows translation along two axes (the X and Z axes), itstrongly resists translation along one axis (the Y axis). Translation ofthe shaft lllll relative to the outer member l2 along the vertical or Yaxis is strongly resisted by the cylinders 14-20. No appreciabletranslation in the Y direction can be made without applying a very largeforce, and then, the bearing assembly would brealr rather thanresiliently deforming. The bearing assembly is useful in a variety ofapplications, including situations where it is necessary to impartforces in one direction (the Z direction) while permitting someflexibility in all other directions.

FIG. 3 is a simplified view of a vibration testing apparatus whichincludes a platform 3th for holding equipment to be vibrated in a mannerthat permits translation in all three axes, X, Y and Z, and pivotingabout the vertical or Y axis. However, the apparatus strongly resistsany pivoting about a horizontal axis (X or Z). That is, the platform 3T1is designed to remain level while undergoing violent vibrations in everymanner that does not require deviation from a level position. Theplatform 341) is supported by four supports 32, 3d, 36 and 38. Eachsupport includes an inner cylinder 4th, an outer cylinder 42 and a post44, the bottom of each post 44lresting on the ground. Each innercylinder d ll extends in a circumferential direction about the platform30, with its axis horizontal and with diametrically opposite sides ofthe cylinder respectively joined to the platform 3(1) and to the outercylinder 42. Each of the outer cylinders d2 is oriented so that its axisis vertical, and diametrically opposite sides of the outer cylinder arerespectively joined to the inner cylinder 40 and to the post 44. Thejoining of the inner and outer cylinders of each support is accomplishedby a cross-shaped coupling member 433 that lies between the cylindersand is fixed to each cylinder along the length of the cylinder.

If the pladorm 3b is pushed up or down, only the inner cylinders 40deflect, and they deflect in the manner of cylinders id and 118 inlFllG. d. The outer cylinders 42 do not deflect in this situation, sincethey strongly resist any up and down movement. Of course, deflection ofonly the inner cylinders dill is sufficient to enable the platform tomove up or down.

if the platform 3 ll is deflected in a horizontal direction along axisX, then all cylinders will deflect except for the inner cylinders of thesupport structures 34 and 38. However, deflection of the other cylindersis sufficient to enable deflection of the platform in the horizontaldirection. in a similar manner, the platform can be deflected along theZ axis. Thus, the platform 3% can be deflected along three orthogonaldirections.

These deflections are resiliently resisted by the cylinders, but theycan readily progress over a limited distance.

The platform 30 can also be pivoted, but only around the vertical or Yaxis. in the case of pivoting about the Y axis, the outer cylinders d2of the four supports deflect in the manner shown in lFlG. 3 for thebearing assembly thereof. However, deflections around the X or Z axesare strongly resisted. if it is attempted to pivot the platform 3% aboutthe X axis, then this would require deformation of the two supportassemblies 32 and 3b in a manner that would be resisted by both innerand outer cylinders of each of these two support assemblies. in asimilar manner, deflection about the Z axis would require deflection ofthe cylinders of the support assemblies 3d and 38 in a manner that wouldbe highly resisted. Accordingly, no appreciable pivoting about the X orZ directions can occur with even a moderately high force. As a result,the platform 3h cannot be deflected away from a level orientation.Vibrations can be applied to the platform in a large number of ways. Forexample, a rotary solenoid can be used with the housing of the solenoidmounted to permit up and down movement and with the vertical-outputshaft of the solenoid connected by a universal coupling to the platform3T1).

lFlG. h is a view of a vibration testing machine constructed inaccordance with another embodiment of the invention. in the machine ofFIG. s, a central platform 6% is employed which is surrounded by anintermediate member 162 and an outer member h s. A first group of fourresilient thin-walled cylinders 66, 653, 741 and '72 with axes extendingsubstantially circumferentially about the platform, connect the platformto the intermediate member 62. A second group of four resilientthin-walled cylinders '74, 7s, 78 and hill), with vertically extendingaxes, join the intermediate member to the outer member. in thisembodiment of the invention, the intermediate member 62 is in acontinuous almost ring-like shape. However, it could be separated intofour segments to provide a machine of the type shown in lFlG. 5. Acontinuous intermediate member is, however, generally preferable toprovide more regular motions and greater strength. In a similar manner,the outer member 64 is shown continuous, and supported by four legs 82on the ground, although it could be constructed as four separate parts.

The vibration of the platform as is accomplished by two bearingassemblies M, hi5 of the type shown in FlG. ll. Each bearing assemblyincludes an outer or surrounding member W or W, an inner shaft M or M,and four thin-walled cylinders coupling the shaft to the surroundingmember. The shafts 92, '94 extend through large openings in theintermediate member 62 and are fixed to the platform 6%. The surroundingmembers 33, 9h extend through large openings 9%, 9 in the outer memberM. Normally, each surrounding member 3%, 3th does not contact the outer,intermediate or platform members 64, (b2, titl, but only the fourcylinders that couple the surrounding member to the shaft within it.Similarly, each of the shafts 32, 9d normally contacts only the platformhill and the four resilient cylinders that couple the shaft to thesurrounding members 3%, 9h.

The vibration of the platform 60 in the direction of arrows 100 isaccomplished by oscillating the surrounding member 88 in the directionof arrows 100. Similarly, the oscillation of the platform 60 in thedirection of arrows 102 is accomplished by oscillating the surroundingmember 90 in the direction of arrows 102. The oscillation of eithersurrounding member 88, 90 can be accomplished by a simple linear drivingdevice such as a solenoid. Each of the bearing assemblies transmitslinear motion to the platform 60 in its longitudinal direction withoutpreventing sideward or up and down deflections of the platform.Referring to FIG. 7, it can be seen that a third bearing assembly 104 isprovided for oscillating the platform 60 in a vertical direction. Thebearing assembly 104 includes a shaft 106 coupled by four thin-walledcylinders to a surrounding member 108 which can be fixed to a solenoidor other vibrating device for up and down motion.

Thus, the invention provides apparatus for supporting a member in amanner that enables vibrations in only selected directions, and whichcan provide a moderate spring force tending to return the member to aneutral position, the spring force increasing in spring constant forlarge vibrations to prevent excessive deflections. A vibration table isprovided which can be supported to maintain a platform in a levelorientation while enabling it to deflect in three orthogonal directionsas well as pivot about a vertical axis. In the case of the levelplatform device, resilient thin-walled cylindrical members are shown forsupporting one member within another. However, instead of usingcylindrical members in this device, it is possible to use elongatedclosed curve looped members of substantially constant cross-section,although if they deviate substantially from a cylinder they may notprovide a substantial spring force tending to return the supportedmember towards its neutral position with a rapidly increasing springconstant.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art and, consequently, it isintended that the claims be interpreted to cover such modifications andequivalents.

What is claimed is:

1. Vibration testing apparatus comprising:

an inner member for holding an article to be vibration tested;

an outer member disposed about said inner member,

said inner and outer members substantially centered on a predeterminedaxis;

a first plurality of flexible substantially cylindrical elementsdisposed between said inner and outer members, each of said cylindricalelements having diametrically opposite sides respectively fixed to saidinner and outer members;

a surrounding member extending substantially coaxially with saidpredetermined axis about said outer member;

a second plurality of flexible substantially cylindrical elements, eachof said second elements positioned between said outer and surroundingmembers and having diametrically opposite sides fixed to said outer andsurrounding members respectively; and

vibration inducing means coupled to said inner on rir i plurality ofcylindrical elements oriented with their axes parallel to saidpredetermined axis and the other plurality of cylindrical elementsoriented with their axes substantially tangent to an imaginary lineextending circumferentially about said predetermined axis.

2. Vibration testing apparatus comprising:

an inner member substantially centered on a predetermined axis;

an outer member extending substantially coaxial with said predeterminedaxis about said inner member;

plurality of bearing assemblies for coupling said inner and outermembers, each assembly including a pair of tubular elements, eachtubular element defining in section a closed curve of substantiallyconstant cross-section;

first element of each pair having opposite sides respectively fixed tosaid inner member and coupled to the second element of the pair, and asecond element of each pair having diametrically opposite sidesrespectively fixed to said outer member and coupled to the first elementof the pair, said first and second elements of each pair extendingperpendicular to each other; and

means for vibrating said inner member.

3. Vibration testing apparatus for vibrating an article to be testedwhile maintaining it in a level orientation comprising:

an inner member for coupling to an article to be tested;

an intermediate member extending substantially coaxial with a verticalaxis about said inner member;

an outer member extending substantially coaxial with said vertical axisabout said intermediate member;

a first plurality of resilient tubular elements defining in sectionclosed loops, said elements having opposite sides respectively joined tosaid inner and intermediate members;

a second plurality of resilient elements defining closed loops, saidelements having opposite sides respectively joined to said intermediateand outer members;

each element of one of said plurality of elements extending vertically,and each element of the other of said plurality of elements extendinghorizontally and substantially tangential to an imaginary line whichextends circumferentially about said central axis; and

means for vibrating said inner member.

4. The apparatus described in claim 3 wherein:

each of said elements is cylindrical.

5. The apparatus described in claim 3 wherein:

said means for vibrating said inner member includes first and secondforce applying means, each including a central shaft attached to saidinner member, an outer part, and a plurality of resilient cylindricalelements with diametrically opposite sides respectively fixed to saidshaft and outer part, the central shaft of said first and second forceapplying means extending substantially at right angles to each other.

1. Vibration testing apparatus comprising: an inner member for holdingan article to be vibration tested; an outer member disposed about saidinner member, said inner and outer members substantially centered on apredetermined axis; a first plurality of flexible substantiallycylindrical elements disposed between said inner and outer members, eachof said cylindrical elements having diametrically opposite sidesrespectively fixed to said inner and outer members; a surrounding memberextending substantially coaxially with said predetermined axis aboutsaid outer member; a second plurality of flexible substantiallycylindrical elements, each of said second elements positioned betweensaid outer and surrounding members and having diametrically oppositesides fixed to said outer and surrounding members respectively; andvibration inducing means coupled to said inner member for vibrating it;one of said first or second plurality of cylindrical elements orientedwith their axes parallel to said predetermined axis and the otherplurality of cylindrical elements oriented with their axes substantiallytangent to an imaginary line extending circumferentially about saidpredetermined axis.
 2. Vibration testing apparatus comprising: an innermember substantially centered on a predetermined axis; an outer memberextending substantially coaxial with said predetermined axis about saidinner member; a plurality of bearing assemblies for coupling said innerand outer members, each assembly including a pair of tubular elements,each tubular element defining in section a closed curve of substantiallyconstant cross-section; a first element of each pair having oppositesides respectively fixed to said inner member and coupled to the secondelement of the pair, and a second element of each pair havingdiametrically opposite sides respectively fixed to said outer member andcoupled to the first element of the pair, said first and second elementsof each pair extending perpendicular to each other; and means forvibrating said inner member.
 3. Vibration testing apparatus forvibrating an article to be tested while maintaining it in a levelorientation comprising: an inner member for coupling to an article to betested; an intermediate member extending substantially coaxial with avertical axis about said inner member; an outer member extendingsubstantially coaxial with said vertical axis about said intermediatemember; a first plurality of resilient tubular elements defining insection closed loops, said elements having opposite sides respectivelyjoined to said inner and intermediate members; a second plurality ofresilient elements defining closed loops, said elements having oppositesides respectively joined to said intermediate and outer members; eachelement of one of said plurality of elements extending vertically, andeach element of the other of said plurality of elements extendinghorizontally and substantially tangential to an imaginary line whichextends circumferentially about said central axis; and mEans forvibrating said inner member.
 4. The apparatus described in claim 3wherein: each of said elements is cylindrical.
 5. The apparatusdescribed in claim 3 wherein: said means for vibrating said inner memberincludes first and second force applying means, each including a centralshaft attached to said inner member, an outer part, and a plurality ofresilient cylindrical elements with diametrically opposite sidesrespectively fixed to said shaft and outer part, the central shaft ofsaid first and second force applying means extending substantially atright angles to each other.